Method of using an electronic chemically sensitive resistor array for the differentiation of synthetic and authentic urine specimens

The method uses a device which measures the volatile organic compounds (VOCs) present in headspaces of fluid samples to differentiate between authentic and synthetic urine samples. The method includes the use of a device which includes an array of resistive microchemical sensors. The device may be exposed to samples of synthetic and authentic urine to identify a pattern of VOCs in each, these steps being referred to herein as training the device. The device may then be exposed to a urine sample of unknown authenticity and a pattern of VOCs identified. The pattern of VOCs from the urine sample of unknown authenticity may be compared to those of synthetic and authentic urine. In some embodiments the device is installed in a toilet. The method may be used to identify a false sample provided for a urine analysis intended to screen for use of illicit drugs.